This invention relates to granular organohalide flame retardant additives for use in fabricating flame retarded plastic articles.
It is well know that a great variety of inflammable plastic articles may be rendered flame retardant by incorporating therein an appropriate amount of an organohalide flame retardant. It would be very convenient and desirable for such flame retardants to be capable of uniformly dispersing in the plastic article by simply co-feeding the flame retardant and a thermoplastic resin together to a fabricating machine.
However, there are many problems in the use of powdered or liquid flame retardants as such for said purpose. They tend to produce harmful dust upon handling. Their limited free-flowing property makes their automated continuous metering difficult. Since particle sizes are far different between the powdered flame retardant and the resin pellets, the former may be easily classified from the resin pellets prior to entering the melting zone of a fabricating machine. Thus, it is difficult to achieve uniform distribution of added flame retardants throughout the body of fabricated plastic article. Liquid flame retardants suffer from a similar problem of difficulty of uniform distribution when used in an amount sufficient to impart a desired degree of flame retardance to the inflammable thermoplastic resin.
Attempts have been made to overcome the above problems. One such attempt employs a master batch containing up to about 30% by weight of flame retardant. This method naturally requires addition of a large amount of master batch to the resin. The master batch made from a particular plastic material can only be used as a rule in fabricating articles made of the same kind of plastic material. Another attempt includes the use of pelletized or granulated flame retardants without any binder material. However, with the use of conventional dry or wet granulating technique, it is often difficult to obtain granules having a sufficient strength and a desired particle size distribution.
It is, therefore, a principal object of the present invention to provide pellets or granules of organohalide flame retardants which are free-flowing, having a desirable uniform particle size distribution and a strength so that they are not easily broken or crushed during storage, transportation and handling but are capable of uniformly dispersing in various fabricated plastic articles by simply co-feeding the granulated flame retardant and resin pellets together to a fabricating machine.
Other objects and advantages of the present invention will become apparent as the description proceeds.